I. Field of the Invention
This invention relates generally to an electric switch, and more particularly to an improved design of an electrical safety switch in which the electrical contacts thereof can be closed only upon the insertion of an actuating member of a predetermined shape through one or more apertures formed in the switch housing.
II. Discussion of the Prior Art
So that certain electrical devices, such as building elevators, power tools and related equipment, can only be operated by authorized personnel, it had been found convenient to equip those devices with safety switches which can only be operated to close an electrical circuit upon the introduction of a specially shaped "key" through an opening in the switch housing. Such an electrical switch is described in the Schulz U.S. Pat. No. 4,524,251, which patent is assigned to the same assignee as the present application. That patent describes an electrical switch in which a housing is provided having three chambers, one of which includes a set of normally-open electrical contacts which can be bridged or closed by the actuation of a spring-biased push rod on which the bridging contacts are mounted. This push rod passes through a set of sealing bellows contained within a second chamber of the switch housing and into a third chamber containing a pair of cam rollers which, when appropriately actuated by a generally U-shaped tool, causes reciprocating motion of the push rod to close the normally-open contacts. One or more openings are provided in the switch housing proximate the roller chamber through which the U-shaped actuating member may be introduced. If an actuating member of a shape differing from the predesigned one is pushed in through one of the housing openings, the cam rollers are locked and cannot cause a switch closure. When the appropriate actuating member is used, however, the cam rollers are displaced by that actuating member to the point where they can rotate and thereby move the push rod so as to cause a switch contact closure.
Also related to the present invention is the safety switch assembly disclosed in the Eicker et al U.S. Pat. No. 4,395,608, which is also assigned to the assignee of the instant application.